Research On Gradient Index Lens Containing Silver Ions By Ion-exchange

The gradient index material has important applications in many fields such as photoelectric system, imaging system, fiber coupling system, and integrated-optical system etc. In conventional ion-exchange techniques, we usually use Tl-glass as the ion-exchange substrate in the fabrication of GRIN lenses. Although in Tl-glass we can get greater index change (Δn) by Tl⁺/K⁺ or Tl⁺/Na⁺ ion-exchange, the main problem that inhibits the wider use of Tl⁺ is its high toxicity. It is harmful to people and circumstance in the manufacture processes and applications. We need search a new way to salve this problem.Now, researches on gradient index glass materials containing silver ions are more popular, it is difficult to get glass with high silver content. For this reason, two-step ion-exchange technology including Ag⁺/Na⁺ and Na⁺/Ag⁺ ion-exchange has been used to get gradient index.This paper is based on the research about the gradient index lens containing silver ions, such as the glass composite, the fusion technique, the component of molten salt, the ion-exchangetemperature and so on. We use the SiO₂-Al₂O₃-B₂O₃-Na₂O-RO(CaO, ZnO,MgO)-As₂O₅ ascomposites of the basic sodium glass. The content of Na₂O is approximately in 15-20mol%. Studying the fusion technique of this sodium glass, we fabricated a series of glass which were homogeneous, colorless, and transparent successfully. The sampled glass also is provided with excellent chemical stability and optical properties. After sodium rod-like glass with diameter of 1.8mm was exchanged for 140 hours by immerged in AgNO₃ molten salt at 370℃, diverging gradient index glass lenses with numerical aperture of about 0.5 containing Ag⁺ were obtained. The gradient index lenses we prepared were perfect in imaging applications, and these lenses were slightly colored after exchanged. The transmission rate of the glass after ion-exchanged exceeds 85%. To form a nearly uniform refractive-index An (the silver ions stuffing ), the first exchange step can be carried out for a sufficiently long time. In the second step, silver ions are partially removed in a sodium-containing molten salt to yield the desired profile, then we can get GRIN lenses. Such lens have potentiality to apply in optical communication systems and image devices .